Radial Shaft Seal

ABSTRACT

A radial shaft seal for a shaft to be sealed operating at high rotational speeds and circumferential speeds in both rotational directions has a sealing lip with a first circumferential ring and a second circumferential ring. The first circumferential ring is resting seal-tightly against the shaft to be sealed and seals the medium side. At the side of the first circumferential ring facing the air side, there are first return elements that convey leakage medium back to the medium side. The second circumferential ring is provided at the side of the first circumferential ring facing the air side and second return elements are provided at its air side. The second return elements guide medium that has passed underneath the second circumferential ring back underneath the second circumferential ring to the medium side.

BACKGROUND OF THE INVENTION

The invention concerns a radial shaft seal with at least one sealing lipof elastomeric material which, at its inner side facing the shaft to besealed, comprises a first circumferential ring that rests seal-tightlyagainst the shaft and seals relative to the medium side; return elementsarranged about the circumference of the sealing lip, wherein the returnelements are provided at the side of the first ring facing the air sideand convey leakage medium to the medium side independent of therotational direction of the shaft; and at least one secondcircumferential ring that is provided at the side of the first ringfacing the air side.

Radial shaft seals in the form of radial shaft seal rings are knownwhich are used for sealing rotating shafts. The sealing lip of theradial shaft sealing ring is resting under radial force with a firstcircumferential ring against the shaft and seals relative to the mediumside. Should medium have passed underneath the first ring, it isconveyed by the return elements back to the medium side. The returnelements are formed by ribs that extend alternatingly oppositely slantedrelative to the circumferential direction of the sealing lip; the ribsare arranged at the sealing lip bottom side and the medium that hasescaped is returned by them, depending on the rotational direction ofthe shaft, to the first ring and conveyed underneath it in the directiontoward the oil side. By means of the second ring, a sealing actionrelative to the air side is provided.

Such radial shaft seal rings cause problems when the shaft is rotatingat high rotational speeds or at high circumferential speeds. This is tobe understood as rotational speeds of at least 10,000 rpm andcircumferential speeds of at least 25 m/s. At such high rotationalspeeds, the ribs arranged at a slant are not well suited as returnelements for reliable return of the medium that has passed underneaththe first ring.

The invention has the object to configure the radial shaft seal of theaforementioned kind such that it is suitable for higher rotationalspeeds as well as higher circumferential speeds of the shaft to besealed in both rotational directions.

SUMMARY OF THE INVENTION

This object is solved for the radial shaft seal of the aforementionedkind in accordance with the invention in that the second ring comprisesadditional return elements at its air side.

In the radial shaft seal according to the invention, the second ring isprovided with additional (second) return elements at its side which isfacing the air side. The additional (second) return elements ensure thatmedium that has possibly passed underneath the second ring is reliablyreturned to the medium side by passing underneath the second ring. Incombination with the first return elements of the first ring, a veryhigh return efficiency of the radial shaft seal in both rotationaldirections is additionally provided because the additional (second)return elements prevent the generation of a vacuum (generated by thereturn elements of the first ring). The return efficiency as well as thepump action of the radial shaft seal is therefore raised to a very highlevel. The radial shaft seal according to the invention is thereforeexcellently suitable for use in the high speed range in which the shaftsmay rotate at rotational speeds of more than 10,000 rpm, preferablyrotational speeds in a range of approximately 15,000 rpm up to 50,000rpm. Such rotational speeds are desired for electric motors in theautomotive industry in the field of electromobility. The shaft to besealed in such cases is the drive shaft of a transmission or the rotorshaft of the electric machine. Such drive shafts have such highrotational speeds not only in forward travel but also in reverse travel.The circumferential speed in the field of electromobility can amount toa multiple of that occurring for conventional transmission shafts andmotor shafts of conventionally driven vehicles (internal combustionengines). The radial shaft seal according to the invention fulfills theextreme specifications in relation to high rotational speeds, to highcircumferential speeds, and, at the same time, to alternating rotationaldirections of the shaft to be sealed. The radial shaft seal ensures inthese cases a proper sealing action between the medium side and the airside.

The sealing lip of the radial shaft seal according to the invention iscomprised advantageously of elastomeric material and lies areally on theshaft to be sealed. The sealing lip is provided with the first returnelements of the first ring and second return elements of the secondring.

In order to ensure an optimal return of the medium that has passedunderneath the first ring and the second ring, the additional (second)return elements in circumferential direction are advantageouslypositioned approximately at the level of the return elements of thefirst ring.

In order to reliably return the medium which has escaped possiblyunderneath the second ring, the additional (second) return elementsadvantageously extend at least partially at a slant in circumferentialdirection of the sealing lip. Due to this slanted course, it is achievedthat medium is returned in the direction toward the medium side uponrotation of the shaft to be sealed.

Advantageously, the additional (second) return elements are embodied ina sickle shape. Such return elements can be produced in a simple andinexpensive way and ensure in both rotational directions of the shaft tobe sealed a reliable return of the medium in the direction toward themedium side.

In a preferred embodiment, the additional (second) return elementsadjoin approximately tangentially the second ring. Thereby, the returnaction of the medium is assisted in an advantageous way.

In a constructively simple configuration, the additional (second) returnelements are formed as one piece together with the second ring.

In an advantageous embodiment, the additional (second) return elementsdelimit pressure chambers together with the neighboring region of thesecond ring. Upon return of the medium that has passed underneath thesecond ring, this medium reaches this pressure chamber which, due to theslanted position of the return elements, tapers toward the second ringin flow direction of the medium to be returned. In this way, such apressure is generated in the respective pressure chamber that the secondring is minimally flowed across by the medium to be returned and areturn mechanism is provided at a defined location.

Preferably, the pressure chambers are positioned at a spacing one afterthe other in circumferential direction of the radial shaft seal. In thisway, a reliable return of the medium is ensured about the entirecircumference of the radial shaft seal.

The pressure chambers are advantageously provided at both end regions ofthe additional return elements. In this context, the pressure chambersof the second return elements taper advantageously in the directiontoward each other. In this way, it is achieved that, depending on therotational direction of the shaft to be sealed, the medium to bereturned reaches one or the other pressure chamber.

In an advantageous embodiment, the additional (second) return elementsare formed by raised portions at the inner side of the sealing lipfacing the shaft.

When the additional (second) return elements are embodied in anadvantageous manner mirror-symmetrical in relation to a correspondingaxial plane of the radial shaft seal, an optimal return is provided inboth rotational directions of the shaft to be sealed.

The return efficiency or pump action is increased in an advantageousmanner when the return elements of the first ring and the additional(second) return elements of the second ring extend approximatelyparallel to each other.

In an advantageous embodiment, the second ring is provided, at its sidewhich is facing the medium side, with bulges that are distributed aboutits circumference and extend in the direction toward the first ring. Dueto the bulges, possible leakage flows are returned again in a targetedand active way to the return elements. The bulges have thus the functionof guiding ribs which guide the medium to the return elements.

So that the return of the medium is ensured about the circumference ofthe sealing lip, the bulges and the depressions are advantageouslyarranged alternatingly in the circumferential direction of the sealinglip.

The free ends of the return elements of the first ring haveadvantageously minimal spacing from the bulges. Between the returnelements of the first ring and the corresponding side wall of thebulges, small return gaps are formed in this way through which themedium can be guided to the return elements of the first ring.

The subject matter of the application results not only from the subjectmatter of the individual claims but also from all specifications andfeatures disclosed in the drawings and the description. They are, evenif they are not subject matter of the claims, claimed as important tothe invention inasmuch as individually or in combination they are novelrelative to the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention result from the additional claims, thedescription, and the drawings.

The invention will be explained in more detail with the aid of anembodiment illustrated in the drawing.

FIG. 1 shows a radial shaft seal according to the invention in an endview.

FIG. 2 shows a section along the line II-II in FIG. 1.

FIG. 3 shows the detail F in FIG. 2 in an enlarged illustration.

FIG. 4 shows the detail B in FIG. 2 in enlarged illustration.

FIG. 5 shows the detail D in FIG. 2 in enlarged illustration.

FIG. 6 shows the detail E in FIG. 2 in enlarged illustration.

FIG. 7 shows the detail H in FIG. 2 in enlarged illustration.

FIG. 8 shows a section along the line VIII-VIII in FIG. 4.

FIG. 9 shows a section along the line IX-IX in FIG. 3 in enlargedillustration.

DESCRIPTION OF PREFERRED EMBODIMENTS

The radial shaft seal which is described in the following with the aidof an embodiment is embodied as a radial shaft seal ring. It is used inparticular for shafts which in use are subjected to extreme demands inrelation to high rotational speeds, high circumferential speeds, andalternating rotational directions. Such demands are in particular posedin the field of electromobility in the automotive industry. Here,electric motors are used whose shafts may have rotational speeds of morethan 10,000 rpm. For future devices, already rotational speeds in therange of approximately 15,000 to approximately 50,000 rpm are aimed for.When the shafts of such electric motors are drive shafts oftransmissions, the high rotational speeds are not only required forforward travel but also for reverse travel. The radial shaft seal ringdescribed in the following fulfills these specifications.

The radial shaft seal ring has a ring-shaped housing 1 with L-shapedcross section. It has a cylindrical wall 2 (FIG. 8) that is passing atone end into a radially inwardly oriented bottom 3. It is centrallyprovided with a through opening 4 for the shaft to be sealed. Thehousing can be comprised of metallic material but also of a hard plasticmaterial.

The bottom 3 is provided at its outer side with a cover 5 which is alsocompletely or partially covering the wall 2 at the radial outer side.The part of the cover 5 which is covering the wall 2 forms in theinstalled position a static seal of the radial shaft seal ring.Advantageously, the part of the cover 5 which covers the wall 2 isprovided with a profiling 6 which projects past the wall 2 and iscompressed elastically upon insertion of the radial shaft seal ring intoa receiving space. In this way, a proper static sealing action isensured. The wall 2 of the housing 1 is seated with press fit in theinstallation space for the radial shaft seal ring.

The cover 5 surrounds also the rim 7 of the through opening 4 andextends across a portion of the inner side 8 of the housing bottom 3.Also, the cover 5 covers advantageously the end face 9 of the wall 2.

The cover 5 is fixedly connected in a suitable way to the housing 1, forexample, with a corresponding binding system. For example, theconnection can be realized by an adhesive. In case of an elastomericmaterial, the cover 5 can be vulcanized to the housing 1. It isadvantageous when the cover 5 at the outer side of the housing bottom 3is additionally connected with form fit to the bottom 3. The cover 5 atits outer side is provided with cutouts 10 (FIG. 1) distributed aboutits circumference which advantageously are distributed along two ringsabout the circumference of the housing bottom 3.

The radial shaft seal ring is provided with a sealing lip 11 which iscomprised of elastomeric material and which, in the installed position,is resting under elastic deformation with a defined pretension againstthe shaft to be sealed. The sealing lip 11 is advantageously embodied asone piece together with the cover 5 and extends about the innercircumference of the housing 1. In principle, it is possible to providethe cover 5 and the sealing lip 11 as separate parts. This has theadvantage that the sealing lip 11 can be produced of a differentmaterial than the cover 5.

The radial shaft seal ring can be provided with a protective lip (notillustrated) which is also advantageously embodied as one piece with thecover 5 and thus also with the sealing lip 11. The protective lip isthen located at the air side 13 (FIG. 2) of the radial shaft seal ringand prevents an ingress of dirt particles and the like to the sealinglip 11.

In the installed position, the sealing lip 11 is resting with elasticdeformation areally against the rotating shaft. In order to keepfriction and thus wear as minimal as possible, the contact pressure orthe specific radial force at which the sealing lip 11 is contacting theshaft is very minimal and is, for example, in a magnitude ofapproximately 0.01 to 0.3 N/mm.

The inner side 14 (FIG. 9) of the sealing lip 11 which is facing theshaft to be sealed is provided with a structure which will be explainedin the following in detail.

At the free rim, at the inner side 14 of the sealing lip 11, acircumferential ring 15 is provided which is formed at the inner side 14by a raised portion which is approximately semicircular in axialsection. The ring 15 has a minimal spacing from the end face 16 of thesealing lip 11.

At the side which is facing away from the end face 16 of the sealing lip11, a wall surface 17 adjoins the circumferential ring 15 (FIG. 9).Return units 18 are provided at the wall surface 17 and ensure that themedium, in general oil, that flows from the medium side 19 (FIG. 2) ofthe radial shaft seal ring underneath the sealing lip 11 is conveyedback to the medium side 19.

The ring 15 comprises sections 20 which are positioned at a spacing toeach other and form sickle-shaped depressions which have a curvedextension (FIGS. 4, 5, and 6) pointing in direction toward the air side13. The sections 20 are formed each mirror-symmetrical to thecorresponding axial plane, as illustrated in FIG. 6. The sections 20 areformed as one piece together with the ring 15 but have a smaller widththan the ring 15 (FIGS. 5 and 6).

The sections 20 can extend about their entire circumferential lengthwith a continuous curvature. It is however also possible that thesections 20 have at half their length a straight central section.Depending on the configuration of the arc-shaped sections 20, it ispossible to affect the return quality of the return units 18.

In the region in which the two ends of the sections 20 pass into thering 15, return elements 21, 22 extending opposite to each other areprovided which extend angularly in circumferential direction of thesealing lip 11. The sections 20 and the return elements 21, 22 form thereturn units 18.

The sections 20 and the return elements 21, 22, like the ring 15, areformed by raised portions which are projecting from the inner side 14past the wall surface 17 of the sealing lip 11. The return elements 21,22 are positioned at an acute angle relative to the neighboring regionsof the ring 15 and delimit together with them V-shaped pressure chambers23, 24, viewed in plan view according to FIGS. 4 to 6. In thecircumferential direction, they taper in the direction toward thearc-shaped section 20 which extends between the two pressure chambers23, 24. The return elements 21, 22 pass in an arc shape into themedium-side ring 15.

As illustrated in FIG. 5, the return elements 21, 22 are connected toeach other by a narrow rib 25. It extends in circumferential directionand parallel to the medium-side ring 15. Advantageously, the rib 25 isformed as one piece together with the return elements 21, 22.

The arc-shaped section 20 is provided such that at half its length ithas the smallest distance from the rib 25.

The arc-shaped sections 20 are distributed uniformly about thecircumference of the sealing lip 11 (FIG. 2). In the described way, thereturn elements 21, 22 adjoin the sections 20 and delimit together withthe neighboring regions of the medium-side ring 15 the pressure chambers23, 24. The rounded tips 26, 27 of the pressure chambers 23, 24 at bothends of the section 20 are oriented toward each other.

The return unit 18 and the rib 25 form a return device 28. Accordingly,several such return devices 28 are provided at a spacing one after theother about the circumference of the sealing lip 11.

In the region between neighboring return devices 28, a raised guidingrib 29 is provided which is arranged at the inner side 14 of the sealinglip 11 and advantageously has the same height as the medium-side ring15. The guiding rib 29 extends in circumferential direction of thesealing lip 11 and widens, beginning at its two ends. Advantageously,the guiding rib 29 is designed to be mirror symmetrical in relation toits transverse center plane 30 (FIG. 3).

Across its length, the guiding rib 29 has a spacing from the medium-sidering 15. Corresponding to the shape of the guiding rib 29, its spacingfrom the ring 15 at half its length is smallest while it is longest inthe region of the two ends in circumferential direction.

The two ends 31, 32 are positioned approximately at the level of thefree ends of the return elements 21, 22 of the neighboring return units18. The free ends of the return elements 21, 22 have a minimal spacingfrom the ends 31, 32 of the guiding rib 29.

One such guiding rib 29 is arranged, respectively, between the returndevices 28 neighboring in circumferential direction. It is formedrespectively by a bulge of a ring 33 which is provided at the inner side14 of the sealing lip 11 and extends coaxially to the medium-side ring15. Between the rings 15 and 33, the return devices 28 are located.

The ring 33 which may have a curved outer side ensures the sealingfunction in the static state, when the shaft to be sealed is notrotating.

The rings 15, 33, the return units 18, and the guiding ribs 29 havepreferably the same height (FIG. 9). In this way, it is ensured that themedium side 19 can be sealed properly by the ring 15. Medium that hasnonetheless escaped underneath the ring 15 is returned by the returndevices 28 and the guiding ribs 29 in a reliable way. The ring 33, whichis resting seal-tightly in the installed position against the shaft,prevents that the medium from the medium side 19 can reach the air side13.

In contrast to the rings 15, 33, the guiding rib 29 has a flat end face36 (FIG. 9). Since the return devices 28 and the guiding ribs 29, viewedin a projection onto the drawing plane (FIG. 4), are embodiedsymmetrically to the respective center plane 30, they act optimally inboth rotational directions. The medium which has reached a locationunderneath the sealing lip 11 is thus returned reliably to the mediumside 19, independent of the rotational direction of the shaft.

The sections 20, the return elements 21 to 22 as well as the rib 25 haveacross their length a constant axial width (FIG. 5), respectively. Inthis way, a uniform return of the medium in both rotational directionsof the shaft is realized.

The height of the sections 20 can be constant. It is also possible todesign these sections 20 such that their height increases continuouslyfrom both ends so that the sections 20 have the greatest height at halftheir length.

The medium-side ring 15 has a minimal spacing from the end face 16 ofthe sealing lip 11. In the installed position, the end face 16 ispositioned approximately at a right angle to the surface of the shaft.Approximately at the level of the medium-side ring 15, acircumferentially projecting ring 37 is provided at the surface of thesealing lip 11 (FIG. 9). It has advantageously a curved surface. Inaxial section (FIG. 9), the ring 37 is designed to be approximatelysemicircular. The ring 37 can contribute to an optimization of thecontact force distribution and/or the magnitude of the contact force ofthe sealing lip 11.

In the illustrated and described embodiment, the return units 18 as wellas the guiding ribs 29 are embodied symmetrical to the transverse centerplane 30. However, it is in principle also possible to design the returndevices 28 to be asymmetric, in deviation from the illustrated preferredembodiment. Such a configuration is beneficial when the shaft to besealed has a main rotational direction in use. In this case, the returndevices 28 and the guiding ribs 29 can be designed such that an optimalreturn action of the medium that has passed underneath the sealing lip11 can be achieved in this main rotational direction. When the shaftthen rotates in the other direction, the return action of theasymmetrically embodied return devices 28 and guiding ribs 29 issufficient in this case.

At the side of the ring 33 which is facing the air side 13, additional(second) return elements 38 are provided which, in the illustratedembodiment, have a sickle shape and are advantageously embodied as onepiece together with the ring 33. The second return elements 38 arelocated, viewed in circumferential direction, at the level of thesections 20 of the medium-side ring 15, respectively. The second returnelements 38 adjoin approximately tangentially the side of the ring 33facing the air side 13 (FIG. 5).

As can be seen in FIG. 5, the return elements 38 have a continuouscurvature and adjoin at half their length the ring 33. The two ends 39,40 are positioned approximately at the level of the ends 31, 32 of theguiding ribs 29 neighboring in circumferential direction.

The sickle-shaped return elements 38 increase the return efficiency ofthe radial shaft seal even for alternating rotational movement of theshaft.

The return elements 38 must not be embodied in a sickle shape but canalso have the shape of angular momentum webs which in circumferentialdirection of the radial shaft seal have alternating slanted positions.

The return elements 38 are located in the air-side region of the sealinglip 11 resting against the shaft and are positioned in the installedstate at a particular angle relative to the shaft which can amount to upto approximately 60°.

The number of return elements 38 is derived preferably from the numberof the return units 18 or return devices 28 located at the medium side.They are arranged in the leading region of the sealing lip 11 restingagainst the shaft.

Between the ends 39, 40 of the return elements 38 and the neighboringends 31, 32 of the guiding ribs 29 flow-through regions 41, 42 areformed through which the medium can flow in a way to be described in thefollowing.

The flow-through regions 41, 42 taper respectively in the directiontoward the ring 33.

Since the return elements 38 are arranged almost in extension to thereturn units 18 or return devices 28, viewed in axial direction, anadditional active return of the medium is provided by means of thereturn elements 38 so that the pump action of the radial shaft seal isincreased and brought to a very high level. In this way, the radialshaft seal can be used excellently in high speed applications.

In order to minimize noise which, for example, may occur in operation atvery high rotational speeds, the length of the return elements 21, 22and/or of the return elements 38 can be varied. The radial shaft seal ischaracterized therefore by an excellent noise reduction when in use. Inaddition, the radial shaft seal is constructively simple in itsconfiguration and can be manufactured inexpensively.

It is further possible to arrange the return devices 28 and/or thereturn elements 38 in circumferential direction of the sealing lip 11such that they adjoin each other immediately and not, as in theillustrated embodiment, at a minimal circumferential spacing relative toeach other.

Upon use of the radial shaft seal, a hydrodynamic flow in the directionof the arrows illustrated in FIG. 5 is produced in the pressure chambers23, 24 due to the medium to be sealed that has passed underneath thering 15. Since the pressure chambers 23, 24 are tapering in flowdirection, a pressure is generated in the pressure chambers 23, 24 thatcause the ring 15 to be able to briefly lift off the shaft in the regionof these pressure chambers so that the medium to be sealed can flow fromthe pressure chambers 23, 24 across the ring and back to the medium side19. This conveyance back to the medium side 19 in the region of thepressure chambers 23, 24 is illustrated in FIG. 5 by the flow arrows 43.

The medium which is passing underneath the ring 15 flows incircumferential direction along the flow arrows 44 (FIG. 5) along theguiding ribs 29 and the medium-side ring 33. As illustrated in FIG. 5,this part of the medium flows in the region between the ring 33 and theribs 25. The return elements 21, 22, which extend in the view accordingto FIG. 5 at an angle to the ring 33, end at a spacing relative to thering 33 so that the medium can flow through between the return elements21, 22 and the ring 33.

The medium that has passed underneath the ring 33 is caught in the flowregions 41, 42 and is guided underneath the ring 33 again in thedirection to the medium side 19.

By widening the region 45 of the return elements 21, 22 in comparison tothe region 46 at the transition of the return elements 21, 22 into thering 15 (FIG. 5), the typical contact pressure distribution of sleeveseals can be counteracted. This has the result that leakage flow in thedirection of the ring 33 is exposed to a higher resistance than thereturn of the medium in the direction of the flow arrows 43.

The widened portion 46 is provided at the transition from the returnelements 21, 22 into the sections 20. In relation to the two widenedportions 45, 46, reference is being had expressly to FIG. 5 in whichthese conditions are schematically illustrated.

The described radial shaft seal is characterized in that the sealing lip11 at the medium side rim is provided with the circumferential ring 15which comprises the sections 20 uniformly distributed about thecircumference. They form recesses or depressions which are pointingtoward the air side 13. The return elements in the form of the sections21, 22 which produce alternating angular momentum are arranged centeredrelative to the recesses 20. The sections 20 end approximatelytangentially at the ring 15. The ring 33 which is facing the air side 13serves for securing the static sealing action. The return elements 38which are arranged at the air side of the ring 33 are also uniformlydistributed about the circumference of the radial shaft seal and arepositioned respectively at the level of the return devices 28. Thereturn elements 38 ensure that medium that has passed underneath thering 15 and underneath the ring 33 is returned to the medium side 19.The interaction of the return devices 28 with the return elements 38leads to an optimal active return action of the medium and thus a veryhigh pump action of the radial shaft seal.

The guiding ribs 29 are also distributed about the circumference of theradial shaft seal. Their number corresponds to the number of thesections 20. The sections 20 and the guiding ribs 29, viewed in radialdirection according to FIG. 5, are embodied to be oppositely curvedrelative to each other and are provided alternatingly in circumferentialdirection of the radial shaft seal.

The guiding ribs 29 form bulges and ensure that the medium which is notreturned by one of the return elements 21, 22 is guided actively to theneighboring return element 21, 22. This additional active supply ofmedium to the return elements 21, 22 increases the return action to themedium side 19.

The ring 15 with the sections 20 configured as depressions reduces thedisturbance of the flow direction of the medium to be sealed. Due to theinertia of the medium, the leakage flow is thus reduced. This isachieved inter alia in that the flow direction of the medium that ispredetermined by the narrowest gap of the double-convergent gap formedby the pressure chambers 23, 24 is predetermined such that the medium,following the circumferential direction, reaches the medium side 19without active deflection.

Moreover, the contact surface in the region of the potential leakageflow is enlarged. In this way, it is made difficult for a possiblyexisting leakage medium to move across the return elements 21, 22 in thedirection toward the air side 13. The bulges located at the ring 33 inthe form of the guiding ribs 29 guide possibly existing leakage flows ina targeted and active way back to the return elements 21, 22.

Medium which has possibly passed underneath the ring 33 is reliablyreturned by the return elements 38 at the air side 13 in the directiontoward the medium side 19. The flow-through regions 41 into which themedium flows form pressure chambers that taper in the flow direction. Inthis way, a pressure is generated that leads to the ring 33 being ableto lift briefly off the shaft in the region of these pressure chambers41 so that the medium to be sealed can flow underneath the ring 33 backto the medium side 19.

In another rotational direction of the shaft, the flow-through regions42 form the pressure chambers which taper in the flow direction of themedium. The pressure which is produced in this way thus also leads tothe ring 33 in the region of these pressure chambers 42 to briefly liftoff the shaft and enable the medium to flow back to the medium side 19.

The radial shaft seal can be used in all fast rotating applications andfor changing rotational directions of a shaft. The shaft to be sealedcan have high rotational speeds as well as correspondingly highcircumferential speeds. Alternating rotational directions between mediumside 19 and the air side 13 are sealed reliably. The main field ofapplication is the use in the high speed field, preferably inelectromobility for sealing transmission shafts or motor shafts. In thiscontext, the rotational speeds of the shaft can be, for example, in therange of 10,000 rpm to approximately 50,000 rpm.

The radial shaft seal can basically be used also for low rotationalspeeds. Even in the range of the starting rotational speed, the radialshaft seal provides for a proper sealing action.

In deviation from the illustrated embodiment, the radial shaft seal canbe also designed such that it is integrated, for example, into a sealingflange. In this case, the radial shaft seal does not need its ownhousing. For example, the sealing lip can be glued to the sealingflange, vulcanized thereto or fastened in any other suitable way.

The specification incorporates by reference the entire disclosure ofGerman priority document 10 2019 002 953.4 having a filing date of Apr.18, 2019.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

What is claimed is:
 1. A radial shaft seal comprising: at least onesealing lip comprised of elastomeric material and comprising an innerside facing a shaft to be sealed, the at least one sealing lipcomprising: a first circumferential ring arranged at the inner side, thefirst circumferential ring configured to rest seal-tightly against theshaft to be sealed and configured to seal relative to a medium side ofthe radial shaft seal; first return elements arranged about acircumference of the at least one sealing lip and arranged at a side ofthe first circumferential ring facing an air side of the radial shaftseal, the first return elements configured to return leakage medium,independent of the rotational direction of the shaft to be sealed, tothe medium side; and a second circumferential ring arranged at the innerside at the side of the first circumferential ring facing the air sideof the radial shaft seal; second return elements arranged at a side ofthe second circumferential ring that is facing the air side of theradial shaft seal.
 2. The radial shaft seal according to claim 1,wherein the second return elements are positioned in a circumferentialdirection of the at least one sealing lip approximately at a level ofthe first return elements.
 3. The radial shaft seal according to claim2, wherein the second return elements extend at least partially at aslant relative to the circumferential direction of the at least onesealing lip.
 4. The radial shaft seal according to claim 1, wherein thesecond return elements are sickle-shaped.
 5. The radial shaft sealaccording to claim 1, wherein the second return elements adjoinapproximately tangentially the second circumferential ring.
 6. Theradial shaft seal according to claim 1, wherein the second returnelements are embodied as one piece together with the secondcircumferential ring.
 7. The radial shaft seal according to claim 1,wherein each one of the second return elements delimits, together with aneighboring region of the second circumferential ring, pressurechambers.
 8. The radial shaft seal according to claim 7, wherein thepressure chambers of the second return elements are positioned at aspacing one after the other in the circumferential direction of the atleast one sealing lip.
 9. The radial shaft seal according to claim 7,wherein the pressure chambers of each one of the second return elementstaper in a direction toward each other.
 10. The radial shaft sealaccording to claim 1, wherein the second return elements are raisedportions at the inner side of the at least one sealing lip.
 11. Theradial shaft seal according to claim 1, wherein the second returnelements are mirror-symmetrical relative to an axial plane of the radialshaft seal.
 12. The radial shaft seal according to claim 1, wherein thesecond return elements and the first return elements are spaced apartfrom each other in an axial direction of the radial shaft seal.
 13. Theradial shaft seal according to claim 1, wherein the first returnelements and the second return elements extend approximately parallel toeach other.
 14. The radial shaft seal according to claim 1, wherein thesecond circumferential ring comprises bulges arranged at a side facingthe medium side of the radial shaft seal, wherein the bulges aredistributed about a circumference of the second circumferential ring andbulge in a direction toward the first circumferential ring.
 15. Theradial shaft seal according to claim 14, wherein the firstcircumferential ring comprises depressions distributed about acircumference of the first circumferential ring, wherein the depressionsextend in a direction toward the second circumferential ring and arepositioned approximately between neighboring first return elements. 16.The radial shaft seal according to claim 15, wherein the bulges and thedepressions are arranged alternatingly along a circumferential directionof the at least one sealing lip.
 17. The radial shaft seal according toclaim 14, wherein free ends of the first return elements have a minimalspacing relative to the bulges.